In accordance with the reheating method of converting steel from ingot to bloom or slab form after stripping, ingots are charged in the soaking pits of a primary (blooming or slabbing) mill and brought to a uniform temperature of approximately 2400.degree. F. The ingots are removed from the soaking pits and placed on the entry roll table of the primary mill, then passed along a roller table to the reducing stand which shapes the ingots into blooms or slabs. The workpiece (bloom or slab) is advanced toward a shear at the end of the mill roller table. The shear cuts the product to the designated length, cropping sufficient scrap from the two ends of the product, corresponding to what was the top and the bottom of the ingot, to insure the elimination of pipe, porosity, and other similar defects.
The problem of accurately determining the optimum cropping point in hot primary mill products has plagued the steel industry for years. The location of this optimum cropping point is in sound product just beyond the extent of primary pipe, but not into the secondary pipe. Traditionally, locating the crop point was dependent upon the experience and judgment of the crop shear operator. He would often have to shear the product more than one time before he would cut through sound product. This procedure resulted in a waste of the operator's time as well as in a reduction of product yield.
Ultrasonic transducers are commercially available that can scan a relatively cold slab, bloom or billet and reveal any internal non-homogeneous portions of the product as an acoustic couple can be easily achieved with a cold product. The use of ultrasonics in testing steel products at relatively high temperatures is not new. Others have tried ultrasonics but have encountered problems in attempting to achieve a proper acoustic couple between the workpiece and the ultrasonic transducer. Normal production temperatures of 1950.degree. F. (1066.degree. C.) are detrimental to transducers commercially available and therefor proper intimate contact between the product and the transducer to form the acoustic couple was thought to be impossible. Without the necessary acoustic couple an accurate determination of any flaw in the workpeice is impossible.